Photovoltaic (PV) sources have characteristic current verses voltage curves. At low currents, a PV source behaves like a non-ideal voltage source. At high currents, a PV source behaves like a non-ideal current source. At some point in between, maximum power can be delivered from a PV source. The maximum power of the PV source is a function of the level of solar radiation, typically specified in Watts per square meter and the temperature of the PV source, typically specified as the PV module cell temperature. Essentially all photovoltaic power converters dynamically track the composite maximum power point of a number of connected solar PV modules. The process is done with a perturb-and-observe algorithm wherein a PV voltage is set and regulated by adjusting the load on the PV source and the power is observed. The PV voltage is then adjusted slightly and the power is again observed, if the power increases as a result of the PV voltage change, the PV voltage is again adjusted in the same direction, if not the PV voltage is incremented in the opposite direction until the PV maximum power point is captured and the PV voltage is dithered about the PV maximum power point voltage. The tracking is dynamic in order to track rapid changes in radiation due to, for example, fast moving cloud cover.
When the maximum power point of a grounded bipolar PV array is tracked by regulating the pole-to-pole voltage of the array, there will be stability issues when the available power from the monopolar subarrays becomes imbalanced. With a grid-interactive inverter, if the positive subarray is partially shadowed and the negative subarray is in full sun, the voltage on the partially shadowed, positive array will become less than the positive peak voltage of the connected electrical grid, the positive DC inverter bus will collapse and the inverter will shut down.